Transparent soap bars have been on the market for many years. They are considered aesthetically pleasing to the eye. They are generally defined as having sufficient transparency so that fourteen point type can be read through a one-quarter inch thick bar. When properly formulated, they are quite mild but are somewhat deficient in hard water properties. Furthermore, they are fairly soft due to their water content and have poor slough properties. Typical transparent soap bars are described in Kamen U.S. Pat. No. 3,562,167, Jungermann et al. U.S. Pat. No. 4,758,370, and Poper et al. U.S. Pat. No. 4,290,904, which are incorporated herein by reference.
It has been suggested to use alkyl dimethylamine oxides in transparent detergent bars because of their excellent foaming properties (cf. Poper et al. U.S. Pat. No. 4,290,904). However, a satisfactory way of doing this on a commercial scale has not been developed. The problem is that alkyl dimethylamine oxides (e.g., dodecyl dimethylamine oxide) are made by reacting aqueous hydrogen peroxide to form an aqueous solution of the alkyl dimethylamine oxide. In practice it has been reported that such solutions should not exceed about 30 weight percent active alkyl dimethylamine oxides or the solution will form an unstirrable gel preventing completion of this reaction. Commercially lauryl dimethylamine oxide is sold as a 30 weight percent aqueous solution. Use of this 30 weight percent solution of alkyl dimethylamine oxide in formulating a soap bar leads to the introduction of an excessive amount of water into the soap bar. For example, if this bar is formulated to contain 10 weight percent alkyl dimethylamine oxide, it will of necessity contain at least 23.3 weight percent water. Such high water levels lead to a very soft soap bar with an unacceptable slough rate. On the laboratory scale this problem appears to have been circumvented by distilling this water from the alkyl dimethylamine oxide solution to form an anhydrous alkyldimethylamine oxide which can be used in the laboratory preparation of a soap bar as shown in Poper et al. U. S. Pat. No. 4,290,904. However, it is impractical to convert 30 weight percent aqueous solutions of alkyl dimethylamine oxides to a dry product on a commercial scale because of the large amount of water involved. Hence, a need exists for an efficient method of making transparent soap bars which contain an effective amount of alkyl dimethylamine oxide without introducing an excessive amount of water and without the need to perform the arduous removal of water from the commercial alkyldimethylamine oxide solution.